S47

Hexacontium laevigatum Haeckel

Hexacontium laevigatum Haeckel, 1887, p. 193, pl. 24, fig. 6; Benson, 1966, p.154, pl. 4, figs. 4, 5

DESCRIPTION

"Cortical shell generally spherical to subspherical but ovoid or ellipsiodal or with subquadrate outline in several specimens; surface generally smooth except in several specimens with a concentration of short,thin, conical by-spines around one of the six main spines, the larger spine in those tests with one spine larger than the remaining five; pores circular to subcircular, small, equal, as wide as or slightly less than the width of intervening bars, with generally regular hexagonal arrangement, without polygonal frames, 12-16 on the half circumference. Second shell spherical to subspherical, surface smooth to slightly thorny, with subcircular to subpolygonal, subequal pores with subregular arrangement 6-8 on the half circumference. First shell subspherical to subpolyhedral, thin-walled, barely visible in many specimens, with 2-3 large polygonal pores on its half circumference. Six, rarely five or seven, mutually perpendicular radial beams that arise from the surface of the inner shell are heavy and three bladed between the second and third shell and extend beyond the cortical shell as three-bladed, in a few tests conical, spines or thorns. In most specimens the six spines are of nearly equal length, but in several one spine is longer (up to 30mu) and heavier, located at one of the poles of the major axis if the cortical shell is ellipsoidal or ovoid, and surrounded by numerous thin conical by-spines, the remaining five main spines being shorter (as short as 8mu) or present as short thorns. In a few tests one or more of the beams and/or spines are not mutually perpendicular to the others.

..."This species differs from H. enthacanthum Jorgensen by its generally smooth surface, its smaller diameter, the presence of more numerous and smaller, more nearly equal circular pores of the cortical shell, the presence of numerous thin by-spines concentrated at one pole of the shell, and in the presence of unequal main spines in numerous specimens." (from Benson, 1966).

DIMENSIONS "diameter of cortical shell (including average of larger and smaller diameters of ovoid or ellipsoidal shells) 77-103mu of second shell 30-46 mu, of first shell 12-17(; length of main spines 10-65mu." (from Benson, 1966).

Plate 5, figures 2a, b

S48

RECENT DISTRIBUTION

1. Benson, 1966; rare or absent in Gulf of California sediments.

2. Molina-Cruz, 1975, Code S17A; not used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S17A at each station.

3. Robertson, 1975; cf. Hexacontium enthacanthum.